<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>带动画的搜索框</title>
<style>
input[type=text] {
  width: 130px;
  box-sizing: border-box;
  border: 2px solid #ccc;
  border-radius: 4px;
  font-size: 16px;
  background-color: white;
  background-image: url('https://static.runoob.com/images/mix/searchicon.png');
  background-position: 10px 10px; 
  background-repeat: no-repeat;
  padding: 12px 20px 12px 40px;
  -webkit-transition: width 0.4s ease-in-out;
  transition: width 0.4s ease-in-out;
}
input[type=text]:focus {
    width: 100%;

}
</style>
</head>
<body>
    <p>搜索输入框动画：</p>
    <form>
        <input type="text" name="search" placeholder="搜索...">
        </form>
</body>
</html>